SQL Server DATEPART() function -

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today wrote 2 queries on datepart() , different returns below

query #1:

select datepart(day,'2015-07-05')

returns '5', expected.

query #2:

select datepart(day, 2015-07-05)

returns '27', little bit funny, , don't understand how 27 being returned.

the difference between these 2 queries 1 date inside ' ', , other without.

anybody can me out here?

2015-07-05 mathematical expression adds integer 2003. (subtracting 7 2015 gives 2008 subtract 5)

2003 evaluates '1905-06-27' when implicitly cast datetime casting int datetime works same adding number of days base date of 1 jan 1900 (i.e. equals dateadd(day, 2003,'19000101')).

so 27 comes from.

the correct way denote date literals in sql server string '2015-07-05' (iso format - unambiguous newer datetime datetypes) or '20150705' (unambiguous legacy datatypes) or using odbc format { d '2015-07-05' }.


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